After mastering all of your skills (including 120 in Dungeoneering and 500 Player Kills), you will be able to purchase a cape from Prince Brand, located in Lumbridge, prices varying by mode:
It is the best available cape in Soulsplit, and offers the best possable stats. It is also always kept on death and can be customized to a player's liking. The Completionist cape can also be utilized as a shortcut teleport to Edgeville. Simply go to your Equipment Tab, right click the Completionist cape and click Operate.